1B11 Foundations of Astronomy Meteorites Liz Puchnarewicz

1B11 Meteorites Meteorites are pieces of rock and metal that fall to Earth. Almost all (over 30,000 have been recorded) are fragments broken from asteroids during collisions. They take between 0.2 and 100 million years to journey from the Asteroid Belt to Earth. About 30 meteorites come from the Moon and about 30 from Mars. Different types of meteorites can place a chronology on solar system processes, eg accretion and differentiation. They can also be used to investigate the evolution of the Sun’s local neighbourhood.

1B11 Composition Asteroidal meteorites fall into three categories: 1.Stones (mostly silicate rocks) 2.Irons (mostly iron-nickel) 3.Stony-irons (an approximate mixture of 1 and 2) They are then sub-classified according to the type and degree of reprocessing (eg melting and differentiation) Unmelted meteorites provide information about the earliest period of the history of the Solar System. Their composition is close to Solar (apart from H and He!). Melted meteorites have a younger “age”.

1B11 Martian meteorites 37 meteorites originate from Mars. Evidence for their origin is based on their composition, age and abundance of noble gases. Analysis of these meteorites suggest that when water was present on the surface of Mars, it was warm and briny and its flow was restricted. This is consistent with being trapped in enclosed places and flash-flooding. McKay et al (1996) proposed that one contained micro- fossils, although this has not been confirmed.

1B11 Stellar/galactic evolution Interstellar dust grains are trapped within stony, unmelted (chondritic) meteorites. These are mainly nanometer-size diamonds and were deposited into the pre-solar system material by neighbouring stars. These dust grains are formed from supernova-type explosions and go on to form the seeds for the creation of new stars. Thus they can be used to trace back the development of our local evolution – and perhaps the evolution of the Galaxy. Current research indicates that the Sun was formed in a group of stars which included supernovae, novae and planetary nebulae.